Organic EL element

ABSTRACT

An object is to provide an organic EL element which can realize the improvement in the difference of an emission luminance due to the difference of an emission rise time in a plurality of light emitting portions. Segment portions S for determining an emission in a specific shape and wiring portions L for separately supplying electric currents to the segment portions S are formed. An area of the wiring portion L of the segment portion S is enlarged such that an emission luminance in the segment portion S falls within a range of from a minimum luminance to a luminance 30% higher than that.

TECHNICAL FIELD

The present invention relates to an organic EL (electroluminescence)element, and particularly to an organic EL element which can realize animprovement in the difference of an emission luminance due to thedifference of emission rise time in a plurality of light emittingportions.

BACKGROUND ART

As shown in FIG. 3, Japanese patent Laid-Open No. 234681/1993 or thelike discloses an organic EL element in which a transparent electrode 2,an organic layer 3, a back electrode 4 are successively formed on atranslucent insulating substrate 1, and the organic layer 3 isconstituted by, for example, a hole injecting layer, a hole transportinglayer, a light emitting layer, and an electron transporting layer.

In the organic EL element as stated above, a direct current power supplyof several tens of volts is connected to the transparent electrode 2 andthe back electrode 4 to supply an electric current between theelectrodes 2 and 4, so that the organic layer 3 emits light, and thelight is irradiated toward the outside through the substrate 1. Itslight emitting portion is generally determined by the pattern of thetransparent electrode 2, except for a dot matrix type.

That is, as shown in FIG. 4, a display portion D and a wiring pattern Lfor supplying an electric current to this are patterned and are formedon the substrate 1 of glass or the like by using a translucentconductive material such as ITO and by a method such as vapordeposition. The display portion D is formed to be a size larger than thesegment portion (region indicated by a dotted line in FIG. 4) Scorresponding to the emission in a specific shape, and as shown in FIG.3, an insulating layer 5 formed by a suitable measure, such as spincoating or roll coating, using an insulating material such as polyimide,acrylic, or phenol, is positioned between the transparent electrode 2and the organic layer 3. The part of the display portion D other thanthe segment portion S (the part covered with the insulating layer 5) isa part of the wiring portion L, and forms the insulating layer 5 exceptfor the emission in a specific shape. That is, by removing theinsulating layer 5 on the segment portion S, the shape of the segmentportion S has been made the desired emission in a specific shape.

In the organic EL element as stated above, for example, as shown in FIG.4, in a case where seven segment portions S1 to S7 are arranged in theshape of a the numeral 8 to express the figures 0 to 9, display portionsD1 to D7 including the segment portions S1 to S7 and wiring portions L1to L7 respectively connected to them are formed, and current supplysources (not shown) are separately connected to the wiring portions L1to L7.

Incidentally, in a case where a pattern is adopted such that the segmentportions S1 to S6 are arranged clockwise, the segment portion S7 isarranged at the center, and all the wiring portions L1 to L7 connectedto these are led out downward, the wiring portions L1, L2, and L6(former group) of the segment portions S1, S2 and S6 positioned abovehave the extension distances longer than the wiring portions L3 to L5and L7 (latter group) of the segment portions S3 to S5 and S7 positionedbelow, and the capacitance becomes larger.

By this, there is a case where the ratio of the capacitance of thesegment portions S1 to S7 to the capacitance of the wiring portions L1to L7 is much different between the former and the latter, and since itis known that an emission rise time depends on the capacitance greatly(for example, see column 0026 of Japanese Patent Laid-Open No.29080/1993), and there are cases where differences in the emission risetime occur among the segment portions S1 to S7.

The difference of the emission rise time converts into difference ofemission luminance in the segment portions S1 to S7, and the displayquality is lowered. Especially in the case of such a structure that anelectric current is supplied by pulse driving to controlemission/non-emission of the segment portions S1 to S7, when thefrequency of the pulse or the duty ratio is changed to adjust theemission luminance to a desired value, in the case where the frequencyis high or the pulse width is short, there is a case where the segmentportions S1, S2, and S6 connected to the former and having a longemission rise time do not emit light.

In the present invention, attention is paid to such problems, and itsobject is to provide an organic EL element which can realize animprovement in the difference of emission luminance due to thedifference of an emission rise time in a plurality of light emittingportions.

DISCLOSURE OF THE INVENTION

As set forth in claim 1, the invention is an organic EL elementcomprising a transparent electrode positioned on a non-emission surfaceof a translucent substrate, a luminous organic layer positioned on thetransparent electrode, and a back electrode positioned on the organiclayer and facing the transparent electrode, the transparent electrodeformed with a plurality of segment portions for determining an emissionin a specific shape and a plurality of wiring portions for separatelysupplying electric currents to the respective segment portions, and ischaracterized in that the area of the wiring portion of the segmentportion having a high emission luminance is enlarged such that theemission luminance of the segment portion falls within a range of from aminimum luminance in the segment portions to a luminance 30% higher thanthat.

Besides, as set forth in claim 2, an organic EL element comprises atransparent electrode positioned on a non-emission surface of atranslucent substrate, a luminous organic layer positioned on thetransparent electrode, and a back electrode positioned on the organiclayer and facing the transparent electrode, the transparent electrodeforming a plurality of segment portions for determining an emission in aspecific shape and a plurality of wiring portions for separatelysupplying electric currents to the respective segment portions, and ischaracterized in that the segments are arranged in a shape of a numeral8, and the wiring portion of the segment portion having a high emissionluminance is extended into an inside of a display of the numeral 8 ofthe segment portions to enlarge an area of the wiring portion such thatthe emission luminance of the segment portion falls within a range offrom a minimum luminance in the segment portions to a luminance 30%higher than that.

Especially, in addition to claim 1 or 2, as set forth in claim 3, afeature is that an insulating layer is positioned between the wiringportions of the transparent electrode and the organic layer.

Besides, as set forth in claim 4, an organic EL element comprises atransparent electrode positioned on a non-emission surface of atranslucent substrate, a luminous organic layer positioned on thetransparent electrode, a back electrode positioned on the organic layerand facing the transparent electrode, the transparent electrode forminga plurality of segment portions for determining an emission in aspecific shape and a plurality of wiring portions connected to aconstant current source and for separately supplying electric currentsto the respective segment portions, and an insulating layer formedbetween the wiring portions and the organic layer except for the lightemitting shape, and is characterized in that the segments are arrangedin a shape of a numeral 8, and the wiring portion of the segment portionhaving a high emission luminance is extended to a place inside a displayof the numeral 8 of the segment portions and covered with the insulatinglayer to enlarge an area of the wiring portion such that the emissionluminance of the segment portion falls within a range of from a minimumluminance in the segment portions to a luminance 30% higher than that.

Besides, as set forth in claim 5, an organic EL element comprises atransparent electrode positioned on a non-emission surface of atranslucent substrate, a luminous organic layer positioned on thetransparent electrode, and a back electrode positioned on the organiclayer and facing the transparent electrode, the transparent electrodeforming a plurality of segment portions for determining an emission in aspecific shape and a plurality of wiring portions for separatelysupplying electric currents to the respective segment portions, and ischaracterized in that a capacitance of the wiring portion of the segmentportion having a high emission luminance is increased such that theemission luminance of the segment portion falls within a range of from aminimum luminance in the segment portions to a luminance 30% higher thanthat.

Besides, as set forth in claim 6, an organic EL element comprises atransparent electrode positioned on a non-emission surface of atranslucent substrate, a luminous organic layer positioned on thetransparent electrode, and a back electrode positioned on the organiclayer and facing the transparent electrode, the transparent electrodeforming a plurality of segment portions for determining an emission in aspecific shape and a plurality of wiring portions for separatelysupplying electric currents to the respective segment portions, and ischaracterized in that an area of the wiring portion of the segmentportion having a low emission luminance is decreased such that theemission luminance of the segment portion falls within a range of from amaximum luminance in the segment portions to a luminance 30% lower thanthat.

Especially, in clam 6, as set forth in claim 7, a feature is that aninsulating layer is positioned between the wiring portions of thetransparent electrode and the organic layer.

Besides, as set forth in claim 8, an organic EL element comprises atransparent electrode positioned on a non-emission surface of atranslucent substrate, a luminous organic layer positioned on thetransparent electrode, and a back electrode positioned on the organiclayer and facing the transparent electrode, the transparent electrodeforming a plurality of segment portions for determining an emission in aspecific shape and a plurality of wiring portions for separatelysupplying electric currents to the respective segment portions, and ischaracterized in that a capacitance of the segment portion having a lowemission luminance is decreased such that the emission luminance of thesegment portion falls within a range of from a maximum luminance in thesegment portions to a luminance 30% lower than that.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram for explaining an equivalent circuit of anorganic EL element in an embodiment of the invention;

FIG. 2 is a plan view for explaining a transparent electrode of the sameas the above;

FIG. 3 is a main part sectional view for explaining a structure of anorganic EL element; and

FIG. 4 is a plan view for explaining a transparent electrode of the sameas the above.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described on the basis of an embodimentshown in the accompanying drawings, however, the same or equivalentportions as the prior art are designated by the same symbols and thedetailed explanation is omitted.

FIG. 1 shows an equivalent circuit of a segment portion Sn (n=1 to 7,the same shall apply hereinafter) as one of segment portions S1 to S7shown in FIG. 2, in which Csn denotes a capacitance of an arbitrarysegment portion Sn, Cln denotes a capacitance of an arbitrary wiringportion Ln (including a portion covered with an insulating layer 5except for the segment portion Sn of a display portion Dn, the sameshall apply hereinafter), In denotes a value of an electric currentsupplied from a constant current source connected to the wiring portionLn, and J denotes a current density obtained by dividing the currentvalue In by an area Ssn of the segment portion Sn. The current value Inis determined so that the current density J comes to have a constantvalue in the respective segment portions Sn. Incidentally, an area ofthe wiring portion Ln is made Sln.

By the use of a distance ds between electrodes 2 and 4 of the segmentportion Sn, a distance dl between the electrodes 2 and 4 of the wiringportion Ln, a relative dielectric constant ers of the segment portionSn, a relative dielectric constant erl of the wiring portion Ln, acapacitance Cs (=Csn/Ssn) per unit area of the segment portion Sn, acapacitance Cl (Cln/Sln) per unit area of the wiring portion Ln, a lightemission voltage Vem of the segment portion Sn, a vacuum dielectricconstant e0, and a capacitance Ctn (=Csn+Cln) of the whole segmentportion Sn, an emission rise time t becomest=Ctn·Vem/In=(Csn+C1n)·Vem/J·Ssn=(1+(C1n/Csn))·Vem/(J·Ss/Cdn)=(1+(C1n/Csn))·Vem/(J·Ss/Ssn·Cs))=(1+(C1n/Csn))·Vem/(J/Cs).

When an emission luminance is determined, the light emission voltage Vemand the current density J are constant irrespective of the area Ssn ofthe segment portion Sn, and when the structure of the organic EL elementis determined, the capacitance Csn becomes constant in the element, andaccordingly, Vem/(J/Cs) is made a constant α.

From the above, it is understood that the emission rise time t ischanged in accordance with the ratio of the capacitance Csn of thesegment portion Sn to the capacitance Cln of the wiring portion Ln,i.e., Cln/Csn=(er1·e0·(Sln/dl))/(erd·e0·(Sdn/ds))=er1·ds·Sln/ers·d1·Ssn.That is, as the value of Cln/Csn becomes large, the emission rise time tbecomes long, and as the value of Cln/Csn becomes small, the emissionrise time t becomes short.

Here, since the relative dielectric constant ers, er1 and the distanceds, dl are constant in the organic EL element, if erl·ds/ers·dl is madea constant β, then C1n/Cdn=β·(Sln/Ssn), and the emission rise time tbecomes α·(1+β·(Sln/Ssn)).

In the above relational expression, if β·(Sln/Ssn) of the latter part isa value sufficiently smaller than 1, a difference of the emission risetime t hardly occurs. However, the relation as mentioned above isactually hard to produce, and a difference occurs in the emission risetime t, and the problem as described in the prior art occurs.

In order to solve such a problem, by making the ratio of the area Ssn ofthe segment portion Sn to the area Sln of the wiring portion Lnconstant, the emission rise time t in the segment portion Sn can be madetheoretically constant.

Incidentally, as described before, the difference of the emission risetime t causes the difference of the emission luminance, however,according to human optics, the difference is hard to visually recognizein the range where the emission luminance is higher (lower) than theminimum luminance (maximum luminance) by about 20 to 30%. Accordingly,as in this embodiment, in the case where there is no large differenceamong the areas Ss1 to Ss7 of the segment portions S1 to S7, the problemof the difference of the emission luminance due to the difference of theemission rise time t is greatly influenced by a large differenceexisting in the wiring portion Ln, and it becomes a problem between thesegment portions S1, S2 and S6 (former) positioned above and the segmentportions S3 to S5 and S7 (latter) positioned below.

As described before, as the value of Cln/Csn becomes large, the emissionrise time t becomes long, and the value of Cln/Csn becomes small, theemission rise time t becomes short. In this embodiment, if the areas Ssnof the segment portions Sn are substantially equal to each other, thecapacitances Csn become substantially equal to each other, and thecapacitance C11, C12, C16 of the former becomes large as compared withthe capacitance C13 to C15, C17 of the latter, and hereby, the emissionrise time t1 of the former becomes longer than the emission rise time t2of the latter.

Accordingly, in order to uniform the emission rise times tn in thesegment portions Sn, it is conceivable that the emission rise time t2 ismade to approach the emission rise time t1, or to the contrary, theemission rise time t1 is made to approach the emission rise time t2.That the emission rise time t1 is made to approach the emission risetime t2 is to shorten the emission rise time t1, and in order to realizethis, Cln (Sln) is made small, and/or Csn (Ssn) is made large. That thearea Sln is made small is to shorten the wiring portion Ln, and thisreceives restrictions by the arrangement of the segment portion Sn andis not easy. Besides, enlargement of the area Ssn can not be freelycarried out since the shape of the segment portion Sn is determined inaccordance with the design.

Accordingly, in order to uniform the emission rise time t, it isnecessary to make the emission rise time t2 approach the emission risetime t1, that is, to prolong the emission rise time t2, and in order torealize this, Cln (Sln) is made large and/or Csn (Ssn) is made small.However, as described before, enlargement of the area Ssn can not befreely carried out since the shape of the segment portion Sn isdetermined in accordance with the design.

Then, the enlargement of the area Sln is the only way left, and in thisembodiment, the areas S13 to S15 and S17 of the latter wiring portionsL3 to L5 and L7 are enlarged.

In order to enlarge the areas S13 to S15 and S17, a suitable method canbe adopted, for example, their lengths are made longer, or their widthsare made wider.

In FIG. 2, as an example, the shapes of the display portions D3 to D5and D7 are made such that they are extended to a place which is theinside of the display of the segment portions S1 to S7 and is coveredwith the insulating layer, that is, they are extend into the innerregion surrounded by the segment portions S3 to S5 and S7, in which thesegment portions Si to S7 and the wiring portions L1 to L7 are notprovided, and the areas of the display portions D3 to D5 and D7 areincreased, so that the areas S13 to S15 and S17 are enlarged. That is,although the display portions D3 to D5 and D7 include the segmentportions S3 to S5 and S7, that the areas of the display portions D3 toD5 and D7 are enlarged without changing the shapes of the segmentportions S3 to S5 and S7 is substantially to increase the areas S13 toS15 and S17 of the wiring portions L3 to L5 and L7 since the portionsfunction as part of the wiring portions L3 to L5 and L7.

As stated above, the area Sln of the wiring portion Ln of the segmentportion Sn having a small emission rise time t (high emission luminance)is enlarged such that the emission luminance falls within the range offrom a minimum luminance to a luminance higher than the minimumluminance by 30% (preferably, 20%), and as a result, the difference ofthe emission luminance in the whole organic EL element can be made tofall within a range to such a degree that it can not be visuallyrecognized, and the display quality can be improved.

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide an organic ELelement which improves a difference of emission luminance due to adifference of emission rise time in a plurality of light emittingportions, and can improve the display quality of the organic EL element.

1. An organic EL element comprising: an organic layer disposed between atransparent electrode and a back electrode; a plurality of segmentportions as emission sites; and a plurality of wiring portions connectedto a constant current source and for separately supplying electriccurrents to respective segment portions, wherein in order that anemission rise time of each of the segment portions is made constant, aratio of electrostatic capacitance of the segment portion and that ofthe wiring portion is made constant in each of the segment portions. 2.An organic EL element comprising: an organic layer disposed between atransparent electrode and a back electrode; a plurality of segmentportions as emission sites; and a plurality of wiring portions connectedto a constant current source and for separately supplying electriccurrents to the respective segment portions, wherein the segmentportions are arranged in a shape of a numeral 8 and in order that anemission rise time of each of the segment portions is made constant, awiring portion of a segment portion high in emission brightness isextended inside of a display of the numeral 8 to make an area of thewiring portion larger, and thereby a ratio of electrostatic capacitanceof the segment portion and that of the wiring portion is made constantin each of the segment portions.
 3. An organic EL element comprising: anorganic layer disposed between a transparent electrode and a backelectrode; a plurality of segment portions as emission sites; and aplurality of wiring portions connected to a constant current source andfor separately supplying electric currents to the respective segmentportions, wherein in order that an emission rise time of each of thesegment portions is made constant a ratio of an area of the segmentportion and that of the wiring portion is made constant in each of thesegment portions.
 4. An organic EL element comprising: an organic layerdisposed between a transparent electrode and a back electrode; aplurality of segment portions as emission sites; and a plurality ofwiring portions connected to a constant current source and forseparately supplying electric currents to the respective segmentportions, wherein the segment portions are arranged in a shape of anumeral 8 and in order that an emission rise time of each of the segmentportions is made constant, a wiring portion of a segment portion high inemission brightness is extended inside of a display of the number 8 tomake an area of the wiring portion larger, and thereby a ratio of anarea of the segment portion and that of the wiring portion is madeconstant in each of the segment portions.